Conduit with heated wick

ABSTRACT

A conduit for a breathing circuit includes a heater associated, at least in part, with a hydrophilic layer. The purpose of the heater is to evaporate any condensed liquid collecting in the conduit, which is first sucked up by the hydrophilic layer. The heated wick reduces the risk of collected water being passed to the patient and causing choking fits or discomfit. It is preferred that the heated wick lies freely in the conduit to settle at low points in the conduit where condensation may collect.

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 09/886,835 filed on Jun. 21, 2001, now U.S. Pat.No. 6,662,802, and entitled “Conduit With Heated Wick”.

BACKGROUND TO THE INVENTION

1. Field of the Invention

The present invention relates to conduits and in particular to conduitsfor use in a breathing circuit.

2. Summary of the Prior Art

In assisted breathing, particularly in medical applications, gaseshaving high levels of relative humidity are supplied and returnedthrough conduits of a relatively restricted size. Build up ofcondensation on the inside wall of the conduit is a frequent result ofthis high humidity. In the prior art, attempts have been made to reducethe adverse effect of this condensation by either reducing the level ofcondensation or providing collection points in the conduit for drainingcondensed liquid from the conduit. Reducing the condensation hasgenerally been by maintaining or elevating the temperature of the gasesflow and/or of the conduit wall to reduce the formation of condensation.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a conduit, whichwill at least go some way towards improving on the above or which willat least provide the public and the medical profession with a usefulchoice.

In a first aspect the invention consists in a conduit for a breathingcircuit including a heater located within said conduit, said heatercomprising an elongate heating element covered with an inner electricalinsulating layer and at least partially covered with an outerhydrophilic layer, there being no means for direct supply of water orfluid to said hydrophilic layer from outside said conduit.

In a second aspect the invention consists in a breathing circuitincluding an expiratory gases flow path and a heater located within saidexpiratory gases flow path and associated at least in part with aportion of hydrophilic material.

To those skilled in the art to which the invention relates, many changesin construction and widely differing embodiments and applications of theinvention will suggest themselves without departing from the scope ofthe invention as defined in the appended claims. The disclosures and thedescriptions herein are purely illustrative and are not intended to bein any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional elevation of a conduit for the expiratorylimb of a breathing circuit according to the present invention.

FIG. 2 is a cross sectional view of a section of conduit wall accordingto one possible construction.

FIG. 3 is a cross sectional view of a co extrusion die head forextruding a conduit including two longitudinal strips of permeablematerial, similar to the conduit of FIG. 1.

FIG. 4 is a cross sectional elevation of a coaxial breathing circuitaccording to a further embodiment of the present invention incorporatinga heated wick in the expiratory gases flow path.

FIG. 5 is a side elevation in partial cross section of a coaxialbreathing circuit including a heated wick in both the inspiratory andexpiratory gases flow paths.

FIG. 6 is a representation of a breathing circuit with an expiratorylimb fashioned according to the present invention and including a heatedwick according to a further aspect of the present invention.

FIG. 7 is a cut-away perspective view of a heated wick according to afurther aspect of the present invention.

FIG. 8 is a side elevation partially in cross section of an expiratorylimb conduit according to a further embodiment of the present invention.

FIG. 9 is a cross sectional view of a conduit including a heated wickaccording to a further embodiment of the present invention.

FIG. 10 is a cross sectional view of a conduit including a heated wickaccording to a still further embodiment of the present invention.

FIG. 11 is a cross sectional view of a conduit including a heated wickaccording to a still further embodiment of the present invention.

DETAILED DESCRIPTION

The present invention involves the provision of a heated wick within oneof the lengths of conduit making up a breathing circuit. By heated wickwe refer to a heater associated with a hydrophilic layer. The heatedwick is disposed freely within the conduit so that at least part of itlays in low points of the conduit at which condensation accumulates.Accumulated condensation is absorbed by the hydrophilic layer andre-evaporated by heat from the heater.

As seen in FIGS. 1A and 7 the heated wick 100 is comprised of an outerhydrophilic layer 108, covering an inner insulating hydrophobic layer112, which in turn covers a heater element 110. Any water that collectsin the conduit 102 is attracted to and drawn into the hydrophilic layer108, and is then re-vaporised as it is heated by the heater element 110.The intermediate hydrophobic insulating layer 112 is provided toelectrically insulate the inner heater element 110 from the rest of thesystem.

Such a heated wick 100 as shown in FIG. 7 may be constructed bycoextruding the hydrophobic insulating layer 112 and hydrophilic layer108 onto the heater wire 110. Suitable materials for the hydrophiliclayer include polyester or polyurethane foam, or a braid of hydrophilicmaterial e.g cotton. Suitable materials for the hydrophobic insulatinglayer include polypropylene or silicone coatings.

An alternate form for the heated wick is shown in each of FIGS. 1 b, 1 cand 1 d. In FIG. 1 b the heated wick includes a looped back heaterelement 110, coated in a hydrophobic insulating layer 112, and the wholeencased within a hydrophilic surrounding layer 108. In a furthervariation depicted in FIG. 1 c the heater element is an electricalresistance heater and includes a length 120 of higher resistance and alength 121 of lower resistance, insulated from one another and joined attheir remote ends. In a still further variation depicted in FIG. 1 d theheated wick 100 is disposed in the conduit as a simple loop. Each ofthese variations provide both ends of the heated wick at the same end ofthe conduit, allowing a single connection of the heater element to anenergising source. The embodiment of FIG. 1 c has the additionaladvantage that the heater element voltage at the remote end will belower than half the supply voltage, and with appropriate selection canbe very close to zero.

Alternatively the hydrophilic layer 108 may achieve its hydrophilic(water attracting effect), through its physical structure and capillaryaction rather than an inherent property of the material composition. Itis to be understood that references to the outer hydrophilic layer 108throughout the specification may refer to the overall hydrophilic natureof the layer 108. The hydrophilic layer 108 may be constructed from ahydrophilic material composition or alternatively may be constructedfrom water resistant materials but have a physical structure configuredso water ‘soaks’ into or is attracted to the layer 108 through capillaryaction. Alternative constructions of the surrounding hydrophilic layer108 are shown in FIGS. 9 a to 9 d and FIGS. 10 and 11.

For example, as seen in FIG. 9 a the heated wick 100 is comprised of aninner insulating layer 112 which covers a heater element 110. The heaterelement 110 and the insulating layer 112 are encased in an outerhydrophilic layer 108, which is comprised of a braided sheath. Thebraided filaments may be of a water resistant material such aspolyethylene terepythalate (PET), polyethylene or polypropylene. In use,liquid water or condensate is drawn into the spaces between thefilaments of the braided sheath by capillary action thus giving layer108 a water attracting or hydrophilic effect.

An alternative form of the heated wick is shown in each of FIGS. 9 b, 9c and 9 d. The construction shown in FIG. 9 b is analogous to thatdescribed previously and shown in FIG. 1 b, except that the hydrophilicsurrounding layer 108 is a braided sheath similar to that shown in FIG.9 a. A variation of the structure shown in FIG. 9 b is shown in FIG. 9c. In this embodiment the hydrophobic insulating layer 112 encapsulatesboth the positive and negative heater wire strands together.

A further alternative form of the heated wick is shown in FIG. 9 d. Inthis embodiment the heater wire(s) are provided by conductive strands210 which are braided into the braided mesh. In this embodiment a pairof conductive heater wire strands 210 are coated in an electricalinsulating material and braided into a mesh tube in order that theheated wick can attract water to itself through capillary action. Itwill be appreciated that a single heater wire or multiple wires may beadvantageous.

FIG. 9 e show a heated wick embodiment where the positive and negativeheater wires are arranged co-axially. In this embodiment a pair ofheater wires 110, are shown. Each heater wire is surrounded by anelectrical insulating layer 211, and each is arranged co-axially. Anouter water attracting braided sheath 108 surrounds the heater wires togive the construction a wicking effect due to capillary action.

Alternatives to the braided mesh embodiment are shown in FIGS. 10 and11. In these embodiments the outer hydrophilic layer 108 is constructedfrom a water resistant material (for example PET) and attracts waterinto spaces and voids 212 on the outer surface of the layer 108 throughcapillary action. The hydrophilic layer 108, shown in FIG. 10 is formedfrom a partially foamed plastic layer which encases the insulatedconductive wire(s). The outer layer is covered in voids or pores 212, inorder that the heated wick can attract water to itself through capillaryaction. Alternatively, the outer layer may be formed by sintering.Heater element(s) 110 are imbedded in layer 108, and may also include anelectrical insulating layer 213.

An alternative structure of a non-braided layer 108 constructed from awater resistant material is shown in FIG. 11. In this embodiment theouter layer 108 includes a number of grooves and/or fins in order toallow the wick to attract water though capillary action. The grooves maybe substantially axial, annular, helical or knurled in a criss-crossfashion.

The heated wick may also be provided in both the inspiratory andexpiratory conduits. In this case a single length of heated wick may rundown the inspiratory conduit and back up the expiratory conduit, withthe ends of the conduits being insufficiently close proximity to enableeasy electrical connection to both ends.

The heated wick is provided with connections at its ends for connectingto an energising source. The ends of the wick may be directlyelectrically connected to electrical connectors in the connector of thetube or conduit. These connectors may for example be a socket forreceiving a plug from a voltage source. Alternatively the heated wickmay be a fixture of an assisted breathing device, such as a ventilatoror humidifier, and may extend from within the breathing conduitconnection port of the device, or be plugged into a socket within suchport. Many other configurations for supplying power to the heated wickwill also suggest themselves.

The heater element 110 is also effective to supply heat to the gasesstream to reduce the overall level of condensation occurring within theconduit. At the same time any condensation that does occur is sucked upby the wick and re-evaporated by heat from the heater element 110.Accordingly where a heated wick is provided in the inspiratory arm ofthe breathing circuit humidity supplied to the gases stream prior toentry into the breathing circuit is not lost through condensation,instead being re-evaporated by the heated wick. This reduces the totalhumidification load of the breathing circuit as well as eliminating therequirement for conduit drainage ports.

Where the heated wick is provided in the expiratory conduit iteliminates the need for conduit drainage ports. Furthermore it providesadditional advantages when used in conjunction with an expiratoryconduit in which at least a part of the conduit wall is formed from abreathable material. Such an arrangement is shown in FIG. 6.

A breathable material, as used herein, is a material that allows thepassage of water vapour without allowing the passage of liquid water orrespiratory gases. Materials may be breathable due to their composition,physical structure a combination thereof.

One such breathable material is an activated perfluorinated polymermaterial having extreme hydrophilic properties. An example of thispolymer material is marketed under the trade mark NAFION by DuPontFluoro products of Fayetteville USA. This material is useful due to itsextreme hydrophilic properties and due to its ability to be extruded,particularly to be co-extruded in combination with other plasticmaterials.

Alternative materials are also envisaged including:

-   -   (a) Hydrophilic thermoplastics,    -   (b) woven treated fabric products exhibiting breathable        characteristics

The preferred material is a hydrophilic polyester block copolymer formedinto a homogeneous flat film. An example of such a film is sold underthe brand SYMPATEX. This material is particularly suited to thin filmproductions.

An example of application of the conduit with heated wick is shown inFIG. 6. A heater element 110 coated with a hydrophilic layer, runs thelength of the semi-permeable conduit 102 and the inspiratory conduit101. During operation humidified gases are drawn through inspiratoryconduit 101, then flow through the T connector 103, and are thendelivered to the patient (not shown). When the patient expires the gasesflow through the T connector 103, and then flow through the breathableexpiratory conduit 102. The expiratory gases will be almost saturatedwith humidity and as the wall of the breathable expiratory conduit 102will be relatively cool, some portion of the vapour in the gases willcondense and therefore water will collect in the conduit and run towardsthe lowest point 106. As already mentioned such collection of water isundesirable and therefore the heated wick 100 is provided to revaporisethe water that collects. This is particularly important where thebreathable material is one, such as SYMPATEX, which transmits watervapour but does not transmit liquid water. While such materials areadvantageous for their ability to stop harmful bacteria and viruses thisadvantage is offset by their inability to transmit liquid water. Byre-evaporation of any collected water by the heated wick it can betransmitted through the breathable membrane in its vapour state.

Referring to FIG. 1, in one embodiment, the conduit 4 of the expiratorylimb of a breathing circuit is formed having one or more longitudinalstrips 2, 3 of breathable membrane as part of the wall 1 thereof.

Referring to FIG. 8 an alternative embodiment of the expiratory limbconduit is shown in which the entire flexible wall membrane of theconduit is formed from a breathable plastic membrane, extruded and woundhelically with edges of adjacent turns sealed to one another.

Referring to FIGS. 4 and 5, further aspects is shown in which anexpiratory limb conduit according to the present invention is providedas a gases flow path of a coaxial conduit configuration, such thatexpiratory gases and inspiratory gases each flow in one of the innerconduit or the space between the inner conduit and the outer conduit andin use water vapour but not liquid water is transmitted from theexpiratory gases passageway to the inspiratory gases passageway.

Referring to FIGS. 2 & 8, spiral or helical internal (or external)reinforcing members 30, or a series of annular hoop reinforcing members,may be provided outside (or inside) the tubular membrane 6 to providesupport to it. The helical, spiral or hoop supporting members may forexample be formed from polymer plastic materials, such as the materialused in the wall of the conduit (not being the breathable regions), oralternatively may for example be a metal wire support, such as drawnsteel wire.

The conduit shown in FIG. 2 may be formed in any one of a number ofmethods. For example the tubular membrane 6 may be supplied in acontinuous tube. Alternatively it might be supplied in tape form, whichmay result in the conduit of FIG. 8. Supplied as extruded tape 81, themembrane may be wound helically onto a former. The helical supportingrib 30, provided in a breathable molten state is then laid on theoverlap between adjacent turns. The heat from the helical supporting rib30 bonds the two adjacent strips with itself forming a flexibleresilient conduit once cooled.

Referring to FIG. 8 an additional longitudinal reinforcement may beprovided to alleviate the shortcomings of some of the breathablematerials. This reinforcement may be in the form of a plurality ofreinforcing threads 83. The threads 83 run parallel to the length of theconduit and are supported on the helical reinforcing ribs, spanningbetween them. As many threads may be provided. For example eight threadsmay be spaced around the circumference of the tube. The reinforcingthreads 83 stop accidental stretching of the conduit, and providing theyhave some stiffness and the rib spacing is not to large, also reduce anylongitudinal compression of the conduit under negative relative internalpressures.

Referring to FIG. 3 the conduit, such as that shown in FIG. 1, mayalternatively be formed by co extrusion of the breathable material(where the material is a suitable extrudable material) with a plasticmaterial forming the remainder of the conduit wall. A suitable coextrusion die 9 is depicted in FIG. 3 in which a pair of circumferentialsections 7 of the die opening have the breathable plastic materialextruded therethrough, and the remainder sections 8 of the annularextrusion opening have the non permeable plastic wall material extrudedtherethrough.

The purpose of the breathable region or regions of the conduit wall isto allow diffusion of water vapour (and for some materials liquid water)from the expiratory limb of the breathing circuit along the path thereofindependent of specific drain locations. This eliminates the build up ofcondensation within the expiratory limb by drying the humidified gasesduring their flow through the expiratory limb. This furthermore reducesthe humidity of the gases arriving at ancillary equipment, such asfilters, ventilators and the like reducing the risk of condensationaccumulation, thereby improving their operation.

In accordance with a further aspect of the invention, and as exemplifiedin FIGS. 4 and 5 the conduit incorporating one or more longitudinalstrips of breathable membrane may further be incorporated in a coaxialbreathing circuit as a passive humidification device. In particularreferring to the cross section in FIG. 4 the coaxial breathing circuitmay include an outer conduit 11 and an inner conduit 10. Preferably, forheat transfer reasons, the inner conduit 10 carries the inspiratory flowin the space 12 there within. The expiratory flow is carried in thespace 13 between the inner conduit 10 and the outer conduit 11, and adoubled back heated wick 100 is provided in the expiratory flow space.The airflow configuration is indicated by arrows 20, 19 respectively inFIG. 5.

The inner conduit 10 is formed having one or more longitudinal strips 2,3 of breathable membrane in the wall 1 thereof, as has previously beendescribed with reference to FIGS. 1, 2 and 3. Thus humidity in theexpiratory flow space 13 may pass through the sections 2, 3 ofbreathable membrane to humidify the inspiratory flow in inspiratory flowspace 12.

The breathable membrane works on relative partial pressures of watervapour so, with the flows in a counter flow arrangement substantialpassive humidification of the inspiratory flow can be achieved.

Referring to FIG. 5 a circuit configuration including the coaxialconduit depicted in FIG. 4 is represented, but with a heated wick 100disposed in both of the inspiratory and expiratory flow paths (forexample doubling back at the patient end connector 15). In this circuitthe conduit has a patient end connector 15 and a ventilator endconnector 16 having inspiratory port 17 and an expiratory port 18. Theinspiratory 20 and expiratory 19 counter flows are indicated.

So in its broadest form the invention is a conduit for a breathingcircuit which includes a heater associated, at least in part with ahydrophilic layer to attract liquid water or condensate to itself. Thepurpose of the heater is to evaporate any condensed liquid collecting inthe conduit. The heated wick is not a humidifier and so no liquid issupplied directly to the hydrophilic material from outside said conduit.The heated wick reduces the risk of collected water being passed to thepatient and causing choking fits or discomfit. It also improves thepredictability of the humidity levels in the gases passed to thepatient. It is preferred that the heated wick lies freely in the conduitto settle at low points in the conduit where condensation may collect.

Where the conduit in question is an expiratory conduit, or at leastwhere the heated wick is located in an expiratory flow path of abreathing circuit, then the heated wick will have additional benefitswhere the conduit has at least of potion of its wall formed frombreathable material for passive dehumidification of the expired gases.Because the breathable material will pass only vapour, evaporation ofany condensed liquid within the conduit will allow that liquid tosubsequently be passed.

Another aspect to the invention is the construction of the heated wick,which is preferably an elongate heating element covered with an innerhydrophobic insulating layer co-extruded with an outer hydrophiliclayer.

It will be appreciated that the concepts encapsulated by the describedand illustrated embodiments are not restricted to being combined only asdescribed. For example the heated wick described with reference to FIGS.6 and 7 may be used in the coaxial conduit of FIGS. 4 and 5 or theseparate limbed conduit as in FIG. 6. Similarly the conduitincorporating the breathable membrane, whether it be the inner conduitof the coaxial configuration shown in FIGS. 4 and 5 or the stand aloneexpiratory limb of FIG. 6, may be formed as a co-extrusion as in FIGS. 1and 3 or as an extruded tape as in FIG. 8 and with the breathablemembrane being of a number of alternate materials. While someembodiments have been described as preferred and convey particularadvantages over other embodiments many other combinations may provecommercially useful.

1. A conduit for a breathing circuit including a heater located withinsaid conduit, said heater comprising an elongate heating element coveredwith an inner electrical insulating layer and at least partially coveredwith an outer hydrophilic layer, there being no means for direct supplyof water or fluid to said hydrophilic layer from outside said conduit,said hydrophilic layer being formed so as to absorb water due to itsstructure, wherein said conduit is an expiratory conduit and said heateris located in an expiratory flow path of said conduit and at least alength of said conduit has a conduit wall wherein at least a region ofsaid conduit wall is of a breathable material.
 2. A conduit as claimedin claim 1 wherein said at least a region is or are distributed oversaid length of said conduit.
 3. A conduit as claimed in claim 1, whereinsaid hydrophilic layer is a braided sheath.
 4. A conduit for a breathingcircuit including a heater located within said conduit, said heatercomprising an elongate heating element covered with an inner electricalinsulating layer and at least partially covered with an outerhydrophilic layer, there being no means for direct supply of water orfluid to said hydrophilic layer from outside said conduit, said saidhydrophilic layer being formed so as to absorb water due to itsstructure, said heater lying freely in said conduit to settle over atleast some of its length at low points in said conduit where condensedwater vapour may collect, wherein said conduit is an expiratory conduitand said heater is located in an expiratory flow path of said conduitand at least a length of said conduit has a conduit wall wherein atleast a region of said conduit wall is of a breathable material.
 5. Aconduit as claimed in claim 4 wherein said at least a region is or aredistributed over said length of said conduit.
 6. A conduit for abreathing circuit including a heater located within said conduit, saidheater comprising an elongate heating element covered with an innerelectrical insulating layer and at least partially covered with an outerhydrophilic layer, there being no means for direct supply of water orfluid to said hydrophilic layer from outside said conduit, wherein saidhydrophilic layer is a braided sheath.
 7. A conduit for a breathingcircuit including a heater located within said conduit, said heatercomprising an elongate heating element covered with an inner electricalinsulating layer and at least partially covered with an outerhydrophilic layer, there being no means for direct supply of water orfluid to said hydrophilic layer from outside said conduit, saidhydrophilic layer being formed so as to absorb water due to itsstructure, wherein said hydrophilic layer is a braided sheath.
 8. Aconduit for a breathing circuit including a heater located within saidconduit, said heater comprising an elongate heating element covered withan inner electrical insulating layer and at least partially covered withan outer hydrophilic layer, there being no means for direct supply ofwater or fluid to said hydrophilic layer from outside said conduit, saidhydrophilic layer being formed so as to absorb water due to itsstructure, said heater lying freely in said conduit to settle over atleast some of its length at low points in said conduit where condensedwater vapour may collect, wherein said hydrophilic layer is a braidedsheath.